With the proliferation of electrical and electronic devices now found on moving vehicles, the distribution of electrical energy to these devices must be carefully considered. It is common for some such electronic devices to be operated by auxiliary rechargeable batteries. These auxiliary batteries may be charged from the alternator of the engine while the engine is running and then continue to power various devices when the engine is not running. Often it is imperative that the batteries be fully charged when the engine is shut down, in order that the devices continue to operate for the longest possible time with the engine off.
The alternator may supply the electrical energy for many devices and batteries at the same time. If the energy demands of the various devices vary widely in time, the use of the energy from the alternator may not be optimized, unless some type of actively controlled, variable energy distribution is used.
An example of this non-optimized use, not to be construed as limiting the scope of the invention, is the charging of an auxiliary battery from the pin 7, or ACC pin, of the interface connector, or “7-way connector”, commonly used in tractor-trailer vehicles. The voltage and current derivable from this pin may be used to power the antilock braking system (ABS) on tractor-trailers. This voltage and current are also an attractive source of energy for charging an auxiliary battery, which must be kept fully charged as long as possible and rapidly recharged when depleted, in order to provide reliable backup power for devices. However, SAE Standard J2247 (Society of Automotive Engineers) specifies a minimum voltage at PIN 7 in order to insure sufficient energy supply for the safe and proper operation of the ABS at all times. As a result, the battery charging current available from PIN 7 is limited to a relatively low value and the charging proceeds relatively slowly. On the other hand, the maximum energy requirements of the ABS occur only when the brakes are actually being applied, a relatively rare event. Most of the time, the ABS is not in operation, and its energy requirement is much less than that during operation. It follows that while the ABS is not in use, more energy can be directed to charging the auxiliary battery. The use of a fixed low energy flow to the battery, therefore, as is currently the practice, is not optimal.
To further illustrate this, in one particular use, it has been demonstrated that compliance with SAE Standard J2247 effectively requires the charging current to be limited to 1.25 Amps at all times, in order to cover worst-case operating conditions. At this current it takes 12 hours to fully recharge a particular battery pack. With optimized use of the alternator energy, however, this time can be reduced to 15 minutes.
There is thus a need for a system and method which will charge a battery from an energy source in the least amount of time without adversely affecting the operation of other devices also drawing energy from this source. Previous inventions do not appear to meet this need. PCT application publication WO 99/42331 discloses a device for supplying electrical energy to devices on a vehicle in the event of failure or discharge of auxiliary batteries. The monitoring method employed is distinct from that of the subject invention. U.S. Publication 2003/0210014 discloses a specialized voltage regulator that sits between the alternator and a battery. U.S. Pat. No. 6,700,353 discloses a voltage regulator for the main charging system. Neither of these addresses the problems addressed by the subject invention.